According to Drugs.com, blisters usually last for only a few days. The blister gradually drains while a new layer of skin is formed underneath the blister; the blistered skin itself then peels away.
Some blisters can last for two weeks or even longer, according to Drugs.com. Prolonged presence of blisters occurs when friction or pressure in the area of the blister persists. With only mild irritation of that sort, the blister generally continues to heal. With more significant irritation and friction, the top layer of the skin might rub away, causing the blister to open and ooze the clear fluid it contains. When this occurs, the blister can get infected or become a deeper wound.